Hello, my name is Katelyn Wiggenhorn, and I am an applications engineer at Texas Instruments. I work in our buck converters and controllers business unit. Today, I am going to discuss precision data acquisition systems and the corresponding challenges of the power subsystem.
On this slide, you can see the block diagram on the left of a precision data acquisition system. High-performance stack systems use high-performance ADCs, which require a low noise floor. Consequently, these ADCs are susceptible to noise from the switch mode power supplies in the power subsystem. And the key challenge for this power subsystem is enabling the signal integrity to achieve a best-in-class signal-to--noise ratio, or SNR, bandwidth, and dynamic range.
Here you can see the reference design board of TIDA-01054. In the red box is the power subsystem portion of the PB design. And on the right side, you can see the power tree. This application is powered off a 24-volt rail, which requires a wide input DC-DC converter to provide the various output voltage rails you see here, from 18.55, 5.5, and 3.8 volts.
So here you can see a comparison between using a wire bond DC-DC converter and the LM53635 as the front-end converter to the TI design. And so this is the device that we'll be seeing the 24 input rail. You can see that the SNR has an improvement of about 1 dB, and the dynamic range has an improvement of about 13 dB. On the left side, what you see is that there are spikes throughout the spectral analysis of the wire bond device, and these spikes are not seen in the LM53635 spectral analysis.
In order to understand the reasons for the improved performance with the LM53635, let's take a look at the low noise optimization of this IC and package design. The LM53635 uses a flip chip on lead frame QFN packaging technology. A standard wire bond QFN package uses a wire bond to connect from the silicon dye to the lead frame. Now this wire bond will have its own associated parasitics, and these inductive parasitics will lead to the switch node ringing that you see on the left switch node, ringing at the bottom of the slide.
Now, on the right side, what you see is a flip chip on lead frame QFN package technology. So the silicon dye is actually flipped directly onto the copper bumps, which is directly connected to the lead frame. And what that's doing is, that's eliminating the wire bond and any parasitics associated with the wire bond. So you can see on the right side of the screen, the switch node wave form of a device with no wire bond QFN packaging. So the switch node ringing is completely eliminated. And any emissions or EMI that would occur because of this switch node ringing is also completely eliminated
Here you can see the pinout of the LMS3655, which also matches the pinout of the LM53635. These pinouts have parallel input pins, so input pins on both sides of the device, as well as ground pins on both sides of the device. This allows you to put two high-frequency bypass capacitors at the input, one on each side of the device. And effectively, what you are doing, then, is you're halving your parasitic inductance of the input loop.
Now, remember that with a DC-DC buck converter, the high di/dt loop, which is sensitive to any parasitic inductance, is at the input. So by halving that parasitic loop at the input, you are able to drastically decrease your ringing that you would see on the switch node or even the output. And this will effectively decrease any emissions that you would see, or any sort of signal integrity problems that you could face due to noise interference.
Third, the LM53635 implements a spread spectrum feature. Spread spectrum dithers the switching frequency of the converter in order to lower the peak emissions. So you can see here a comparison of the spectrum of the conducted emission spectrum of the LM53635 on the left without spread spectrum and on the right with spread spectrum. So the peaks actually decreased by about 10 dB. And so when you're looking at your SNR, or signal integrity, you can see that improvement in this spectral analysis before, as we showed.
For more information on this TI reference design or the LM53635, as well as additional wide input power solutions, please use the links on this slide. Thank you for listening. 你好，我是Katelyn Wiggenhorn， 我是德州仪器的应用工程师。 我就职于我们的降压转换器和控制器业务部门。 今天，我将讨论精密数据采集系统 以及电力子系统的 相应挑战。
在此幻灯片中，你可以看到精密数据 采集系统左侧的程序框图。 高性能堆栈系统使用高性能ADC， 这需要低本底噪声。 因此，这些ADC易受来自电源子系统中的 开关模式电源的 噪声的影响。 此电源子系统面临的主要挑战 是实现信号完整性，以实现同类最佳的 信噪比或SNR，带宽和动态范围。
在这里你可以看到TIDA-01054的参考设计板。 在红色框中是PB设计的 电源子系统部分。 在右侧，你可以看到电源树。 该应用由24伏电压轨供电， 这需要一个宽输入DC-DC转换器，以提供 你在此看到的各种输出电压轨，范围为18.55,5.5 和3.8伏。
因此，你可以看到使用引线键合DC-DC 转换器和LM53635作为TI设计的前端转换器之间的 比较。 所以这是我们将看到 24输入轨道的设备。 你可以看到SNR的改善约为1 dB， 动态范围提高了约13 dB。 在左侧，你看到的是 在焊线装置的光谱分析中 存在尖峰，并且在 LM53635光谱分析中没有看到这些尖峰。
为了理解LM53635性能提升的 原因，让我们来看看 这款IC的低噪声优化 和封装设计。 LM53635采用倒装芯片引线框架QFN 封装技术。 标准引线键合QFN封装使用 引线键合从硅染料连接到引线框架。 现在这种引线键合将有自己的相关寄生效应， 这些电感寄生效应将导致你在左侧开关节点上 看到的开关节点振铃， 在滑块底部振铃。 现在，在右侧，你看到的是 引脚框架QFN封装技术的倒装芯片。 因此，硅染料实际上直接 翻转到铜凸块上，铜凸块直接 连接到引线框架。 而这正在做的是，这消除了 引线键合和与引线键合相关的任何寄生效应。 因此，你可以在屏幕右侧看到 开关节点波形的器件没有引线键合QFN封装。 因此完全消除了交换节点振铃。 由于此开关节点振铃 而发生的任何发射 或EMI也完全消除。
在这里你可以看到LMS3655的引脚排列， 它也与LM53635的引脚排列相匹配。 这些引脚分布具有并行输入引脚， 因此器件两侧的输入引脚 以及器件两侧的接地引脚。 这允许你在输入端放置 两个高频旁路电容，器件两侧各一个。 而且，有效的是，你正在做的是 将输入回路的寄生电感 减半。
现在，请记住，使用DC-DC降压转换器时， 对任何寄生电感敏感的高di / dt环路 都在输入端。 因此，通过将输入处的寄生回路减半， 你可以大幅减少在开关节点 甚至输出上看到的振铃。 这将有效地减少 你将看到的任何排放，或由于噪声干扰 而可能面临的任何信号完整性问题。
第三，LM53635实现了扩频功能。 扩频会降低转换器的开关频率， 以降低峰值发射。 因此，你可以在此处看到 LM53635在没有扩频的情况下 左侧的传导发射频谱的频谱 与在右侧的扩频频谱的比较。 因此峰值实际上降低了约10 dB。 因此，当你查看信噪比或信号完整性时， 你可以看到之前的光谱分析有所改进， 正如我们所展示的那样。
有关此TI参考设计 或LM53635的更多信息，以及其他宽输入 电源解决方案，请使用此幻灯片上的链接。 谢谢你的收听。

Description

April 5, 2019

This video discusses the unique challenges of precision data acquisition, and solutions that use wide input, low noise dc-dc converters to optimize the best in class SNR, bandwidth, and dynamic range.